Infectivity and competitiveness for nodulation of N-limited Bradyrhizobium japonicum

LÓPEZ GARCÍA S.L.; FAVELUKES, G.; LODEIRO, A.R.

Foz do Iguaçu, Brasil

Congreso; 12th International Congress on Nitrogen Fixation; 2000

Universidade Federal do Parana, Brasil

Bradyrhizobium japonicum LP 3001 (Spcr) was grown in liquid Götz media either complete (N100), with N-source reduced to 10% (N10) or without N-source (N0). In all three N-conditions, logaritmic growth phase cultures gave around 50% more nodules and their distribution was more concentrated around the root tip position at the time of inoculation than stationary-phase cultures thus showing a higher infectivity. For logaritmic cultures, N0 and N10 were significantly more infective than N100. For stationary cultures, the order was N0>N10>N100. To assess competition, we inoculated B. japonicum LP 3004 (Strr) in vermiculite pots. After 30 days the population had 1.3 107 UFC/ml substrate solution. At this time we planted soybeans in the pots, inoculating each plant with 1.7 108 to 1.3 109 UFC of N0- or N10- or N100-LP 3001 cultures, either logaritmic or stationary. After 25 days, 80% of the nodules were occupied by LP 3004. Competiveness of logaritmic and stationary LP 3001 cultures was very similar, being stationary N100 the best competitor. Thus, N-limitation significantly enhanced infectivity but not competiveness of B. japonicum.